1. Field of the Invention
The invention relates to a honeycomb body, in particular a catalyst body for motor vehicles, including at least partly textured layered metal sheets forming walls of a plurality of channels through which a fluid can flow.
2. Description of Related Art
Many embodiments of metal catalyst carrier bodies of such a type are known and are described, for instance, in Published European Application Nos. 0 220 468 Al, corresponding to U.S. Pat. No. 4,878,746; 0 279 159 Al, corresponding to U.S. Pat. No. 4,845,073; 0 245 737 Al, corresponding to U.S. Pat. No. 4,832,998; or 0 245 736 Al.
It has long been known that in most applications and given the usual dimensions of such honeycomb bodies, the flow in the channels is essentially laminar, because very small channel cross sections are used. Under such conditions, relatively thick boundary layers form at the channel walls, which reduce contact between the core flow in the channels and the walls. Processes of diffusion between the core flow and the boundary layer partly balance this out, but still attempts have long been made to gain improvements with such devices by means of special structuring of the honeycomb body.
For instance, it is known from German Patent DE-PS 1 192 624, corresponding to U.S Pat. No. 3,208,131, to make the honeycomb body from a large number of disks that are disposed in succession and have the channels which are offset from one another in the flow direction. A body that is constructed in that way has a succession of new leading edges in the interior thereof, at which the flow is split. Preferably, disks made of spirally rolled smooth and corrugated metal sheets are used in succession, with the direction of rolling being changed each time. On one hand, such a structure is very expensive from a production standpoint because of the many small disks, and on the other hand it leads to irregular configurations of the channels that are offset from one another, which can be disadvantageous during the coating operation and during later operation.
In Published European Application Nos. 0 152 560 Al and 0 186 801 A2, possibilities for achieving the same concept are described that are more advantageous in production terms, because they do not require assembly of a honeycomb body from a plurality of disks. However, the undulating forms described therein do result in considerable proportions of the surface area of the metal sheets being used contacting one another, and as a result the usable area for catalytic contacting is disadvantageous in proportion to the amount of material being used.
In a survey article by M. Nonnenmann, entitled "Neue Metalltrager fur Abgaskatalysatoren mit erhohter Aktivitat und innerem Strdmungsausgleich" [New Metal Carriers for Exhaust Gas Catalysts That Have Increased Activity and Internal Flow Equalization] ATZ Automobiltechnische Zeitschrift [Automobile Industry Journal] 91 (1989), 4, pp. 185-192, describing the advantages and effects of flow channels that are offset from one another in the flow direction, a variant is also proposed in which instead of a smooth sheet metal layer, a so-called micro-corrugated strip is used, which makes for somewhat more advantageous utilization of the surface area. However, a micro-corrugation strip, along with smooth contacting surfaces, forms tiny channels on other structured sheet-metal strips, which become clogged during a later coating operation and thus result in a considerable increase in pressure loss and a further increase in active surface area as well as an unnecessary consumption of coating composition. Nevertheless, the article shows that because of the production options, a metal catalyst carrier body is superior to an extruded ceramic body, because the flow conditions in the interior can be influenced by structural provisions. An additional effect can arise, namely the transverse mixing of flows in the various channels through corresponding connecting paths or openings in the channel walls.